Starter for a high-pressure gas discharge lamp

ABSTRACT

On one side, a high-pressure gas discharge lamp (10) is connected, by way of the secondary winding (16) of an ignition transformer (14), to a line (11) and, on its second side, to a second line (12). It is therefore connected to a first voltage U 1 . A third line (13) delivers a further voltage U 2 . The ignition energy is supplied with the aid of a pulse. For this purpose, a spark gap (17) is provided in series with the primary winding (15), which gap abruptly becomes conductive when the breakdown voltage is attained. A first capacitor (18) that is charged by the voltage U 2  by way of a resistor (20) connected in series is disposed in parallel to the first capacitor. The series connection of a second capacitor (19) and a diode (22) is provided in parallel to the first capacitor. The connecting point of the second capacitor and the diode is connected to the second line (12) by way of a resistor (21). This second capacitor 19 is charged by the voltage U 1 . The ignition-current path is closed by a voltage-limiting element (23). When the spark gap breaks down, the first, then both, capacitors experience a graduated discharge.

RELATED ART

The invention is based on an ignition apparatus for a high-pressure gasdischarge lamp, particularly for use in headlights of motor vehicles, ofthe type having an ignition transformer whose primary winding can besupplied with a voltage, and whose secondary winding ignites thehigh-pressure gas discharge lamp with the stepped-up value of thevoltage, and wherein a capacitor is provided in parallel to the seriesconnection of the primary winding and a controllable switch or theprimary side, the capacitor is charged when the supply voltage isactivated, and, when a certain voltage is attained, the capacitor isdischarged by the switching on of the controllable switch for releasingthe voltage.

A known ignition apparatus of this type, as described in DE 40 17 415C2, includes an ignition transformer whose primary winding is suppliedwith a voltage. The secondary winding steps this voltage up to thevoltage required to ignite the lamp. On the primary side, a capacitor isdisposed in parallel to the series connection of the primary winding anda controllable switch formed by, for example, a thyristor. For ignition,this capacitor is charged to a voltage that is present and effective atthat time. When a specific voltage is attained, the controllable switchis switched on and the capacitor is discharged for emitting the ignitionpulse.

In this known ignition apparatus, a single capacitor supplies the totalignition energy and the energy required in the critical phase of thetransfer of the high-pressure gas discharge lamp from the ignitionoperation into the burning operation. This capacitor must therefore beable to be charged to a very high voltage level, on the one hand, and,on the other hand, have the necessary capacity. This necessitates acostly and complex component that also has a considerably large spacerequirement.

SUMMARY AND ADVANTAGES OF THE INVENTION

In contrast, the ignition apparatus for a high-pressured gas dischargelamp according to the invention claim 1 has the advantage of improvingthe transfer behavior, because energy can be supplied later in thecritical range of the transition of the high-pressure gas discharge lampfrom the ignition operation to the burning operation. This isadvantageously effected in that the total ignition energy need not bemade available at the high voltage level due to the graduated capacitordischarge. This permits an economical utilization of space in the use ofless expensive and smaller components. This leads to savings in spaceand costs.

In accordance with the invention, this is essentially achieved in that asecond capacitor that is connected in series with a diode is provided inparallel to the capacitor, that this second capacitor can be charged toa lower voltage than the first capacitor, and that this second capacitoris then discharged by way of the correspondingly-polarized diode, andthe switched-on, controllable switch is discharged into the primarywinding if its voltage has become greater than that of the firstcapacitor during its discharge.

In a useful embodiment of the invention, the capacity of the secondcapacitor is approximately 2 to 5 times the capacity of the firstcapacitor.

In an advantageous modification of the invention, the voltage thatcharges the first capacitor is greater, preferably about two to fivetimes greater, than the voltage that charges the second capacitor.

The invention can have two particularly advantageous embodiments. In oneembodiment, the first capacitor can be charged by a separately-suppliedvoltage. This can also be referred to as the 3-conductor concept. In theother embodiment, which is to be referred to as the 2-conductor concept,the second capacitor can be charged by an internally-obtained voltagethat is preferably smaller, by the voltage difference of a Zener diode,than the voltage with which the first capacitor can be charged.

In a further advantageous embodiment of the invention, it is providedthat resistors are connected in series with the two capacitors, whichresistors aid in the selection of the time constants of the charging ofthe capacitors, taking into account the energy necessary for ignitingthe high-pressure gas discharge lamp and its transition into the burningoperation, such that the desired voltage is attained at the secondcapacitor when the controllable switch closes.

In a useful embodiment of the invention, the controllable switch is aspark gap that switches on when a specific voltage has been achieved.

In a further advantageous embodiment of the invention, avoltage-limiting element, e.g. a varistor, is provided between the inputterminals of the ignition apparatus for protecting the voltage supplythat supplies the ignition circuit against surges.

DRAWINGS

The invention is described in detail in the following description by wayof embodiments illustrated in the drawings, wherein:

FIG. 1 is a first embodiment of the ignition apparatus configured inaccordance with the invention, according to the 3-conductor concept, and

FIG. 2 is a second embodiment of the ignition apparatus configured inaccordance with the invention, according to the 2-conductor concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first embodiment of the ignition apparatus configured inaccordance with the invention, which is designed according to the3-conductor concept. A high-pressure gas discharge lamp 10 is connectedon one side to a first connecting line 11 of a current-supply circuit,not shown, by way of a secondary winding 16 of an ignition transformer14. The high-pressure gas discharge lamp 10 is connected on its secondside to a second connecting line 12 of the current-supply circuit. Afirst voltage U₁ is applied between the connecting lines 11 and 12. Athird connecting line 13 supplies a further voltage U₂ between theconnections 11 and 13. The high-pressure gas discharge lamp 10 issupplied with both burning and ignition energy via these threeconnecting lines.

The ignition energy is supplied by the ignition apparatus configured inaccordance with the invention, with the aid of a pulse. For thispurpose, the ignition transformer 14 is provided with a primary winding15 and the secondary winding 16, which are closely coupled to oneanother. A spark gap 17 is provided in series with the primary winding15 as an economical, controllable switch that abruptly becomesconductive when the breakdown voltage is attained, thus generating theignition pulse and permitting the flow of current through the primarywinding 15. A first capacitor 18 is disposed in parallel to the seriesconnection of the primary winding 15 and the spark gap 17. This firstcapacitor 18 is connected in series with a resistor 20 between theconnecting lines 11 and 13, and is thus charged by the voltage U₂. Theseries connection of a second capacitor 19 and a diode 22 is provided inparallel to the first capacitor 18. The connecting point of capacitor 19and diode 22 is connected to the connecting line 12 by way of a resistor21. This second capacitor 19 is therefore in series with the resistor 21between the connecting lines 11 and 12, and is thus charged by thevoltage U₁. The diode 22 is polarized such that its anode is connectedto the connecting point of the second capacitor 19 and the resistor 21,and its cathode is connected to the connecting point of the firstcapacitor 18 and the resistor 20, and to the one connection of the sparkgap 17. A varsity 23 is disposed between the connecting lines 11 and 12for protecting the current-supply circuit, not shown, from surges by theignition transformer 14, and for closing the ignition-current path ofthe high-pressure gas discharge lamp 10.

The function of the above-described embodiment of the ignition apparatusconfigured in accordance with the invention is as follows. Until thebreakdown of the spark gap 17, the first capacitor 18 is charged, by wayof the resistor 20, with the voltage U₂, which is applied to theconnecting line 13 and used only during ignition, and can therefore becharacterized as an auxiliary voltage. At the same time, the voltage U₁,which is applied between the connecting lines 11 and 12 and supplies thetakeover voltage and, later, the burning voltage of the high-pressuregas discharge lamp 10, charges the second capacitor 19 by way of theresistor 21. In this phase, the voltage U₂ is always greater than thevoltage U₁. In an advantageous voltage ratio, the voltage U₂ isapproximately 2 to 5 times the voltage U₁. This blocks the diode 22. Thetime constants for the charging of the capacitors, T1=R₂₀ * C₁₈ for thefirst capacitor 18 and T2=R₂₁ * C₁₉ for the second capacitor 19, areselected through the suitable selection of the resistors 20 and 21 suchthat the desired voltage U_(C2) is achieved at the second capacitor 19if the spark gap 17 switches on. The dimensioning of the capacitors,which has been chosen based on energy considerations, is a factor in theselection of the time constants. Moreover, it is useful to select thecapacity of the second capacitor 19 to be approximately 2 to 5 times thecapacity of the first capacitor 18.

When the spark gap 17 breaks down, a current flux occurs in the primarycircuit comprising the first capacitor 18, the, primary winding 15 andthe spark gap 17. According to the transmission ratio of the ignitiontransformer 14, this current flux generates a voltage in the secondarywinding 16 that leads to the breakdown in the high-pressure gasdischarge lamp 10. Following this breakdown, the light arc in thehigh-pressure gas discharge lamp must be stabilized. In addition, energymust be supplied later. In accordance with the invention, this isparticularly effected in that, when the voltage U_(C1) at the firstcapacitor falls below the value U_(C2) at the second capacitor 19, theenergy stored in the second capacitor 19 is available in addition to theenergy stored in the first capacitor 18, and is stepped up, via theprimary winding 15, by means of the secondary winding 16, thensimultaneously transmitted with the other energy to the high-pressuregas discharge lamp 10. Therefore, according to the invention, the energyrequired during the transition from the ignition of the light arc intoburning operation following the breakdown of the high-pressure gasdischarge lamp 10 is supplied later at a significantly lower voltagelevel due to the graduated capacitor discharge.

FIG. 2 shows a second embodiment of the ignition apparatus configured inaccordance with the invention, which is designed according to theso-called 2-conductor concept. A high-pressure gas discharge lamp 210 isconnected on one side to a first connecting line 211 of a current-supplycircuit, not shown in detail, by way of a secondary winding 216 of anignition transformer 214. The high-pressure gas discharge lamp 210 isconnected on its second side to a second connecting line 212 of thecurrent-supply circuit. A voltage U₁ is applied between the connectinglines 211 and 212. The high-pressure gas discharge lamp 210 is suppliedwith both burning and ignition energy via these three connecting lines.

The ignition energy is supplied by the ignition apparatus configured inaccordance with the invention, with the aid of a pulse. For thispurpose, the ignition transformer 214 is provided with a primary winding215 and the secondary winding 216, which are closely coupled to oneanother. A spark gap 217 is provided in series with the primary winding215 as a controllable switch that abruptly becomes conductive when thebreakdown voltage is attained, thus generating the ignition pulse andpermitting the flow of current through the primary winding 215. A firstcapacitor 218 is disposed in parallel to the series connection of theprimary winding 215 and the spark gap 217. This first capacitor 218 isconnected in series with a resistor 220 between the connecting lines 211and 212, and is thus charged by the voltage U₁. The series connection ofa second capacitor 219 and a diode 222 is provided in parallel to thefirst capacitor 218. The connecting point of capacitor 219 and diode 222is connected to the connecting line 212 by way of the series connectionof a resistor 224, a Zener diode 225 and the resistor 220. Hence, aninternally-generated voltage U₂, which is lower than the voltage U₁ bythe voltage of the Zener diode 225, is applied to the connecting pointof this second capacitor 219 with the diode 222. The diode 222 ispolarized such that its anode is connected to the connecting point ofthe second capacitor 219 and the resistor 224, and its cathode isconnected to the connecting point of the first capacitor 218 and theresistor 220, and to the one connection of the spark gap 217. Avoltage-limiting element 223, e.g. a varsity, is disposed between theconnecting lines 211 and 212 for protecting the current-supply circuit,not shown, from surges by the ignition transformer 214, and for closingthe ignition-current path of the high-pressure gas discharge lamp 210.

The function of the above-described second embodiment of the ignitionapparatus configured in accordance with the invention is as follows,with only the features that differ from the first embodiment beingdiscussed. The second capacitor 219 is charged to the voltage levelU_(C2) with the aid of a portion of the voltage U₁, specifically theinternally-generated voltage U₂. This voltage arises from thesubtraction of the breakdown voltage of the Zener diode 225 from thevoltage U₁. The time constant for the first capacitor 218, T1=R₂₂₀ *C₂₁₈, and the time constant for the second capacitor 219, T2=C₂₁₉ *(R₂₂₀+R₂₂₄), are selected through a suitable selection of the resistors 220and 224 such that the desired voltage U_(C2) is attained at the secondcapacitor 219 when the spark gap 217 switches on. The dimensioning ofthe capacitors 218 and 219, which has been chosen based on energyconsiderations, is a factor in the selection of the time constants.Moreover, it is useful to select the capacity of the second capacitor219 to be approximately 2 to 5 times the capacity of the first capacitor218. The value of the resistor 224 can also be zero.

The function of this embodiment according to the 2-conductor concept isotherwise identical to the function explained in connection with theembodiment of FIG. 1.

An advantage of the ignition apparatus of the invention is that thetotal ignition energy does not need to be made available at the highvoltage level. The graduated capacitor discharge permits economicalutilization of space. Furthermore, the use of inexpensive capacitors ispermitted, and an improvement in the transition behavior is achieved. Inthe critical range of the transfer of the high-pressure gas dischargelamp from the ignition operation into the burning operation, sufficientenergy can be supplied later at the lower voltage level.

We claim:
 1. Ignition apparatus for a high-pressure gas discharge lamp,particularly for use in headlights of motor vehicles, having an ignitiontransformer, whose primary winding can be supplied with a supplyvoltage, and whose secondary winding ignites the high-pressure gasdischarge lamp with the stepped-up value of the voltage, wherein a firstcapacitor is provided in parallel to the series connection of theprimary winging and a controllable switch on the primary side, the firstcapacitor is charged when the supply voltage (U₁) is activated, and,when a certain voltage is attained, the first capacitor, is dischargedby the switching on of the controllable switch for releasing thevoltage; and wherein: a second capacitor connected in series with adiode is provided in parallel to the first capacitor; circuit means areprovided for charging this second capacitor to a lower voltage than thefirst capacitor; and this second capacitor is then discharged, via theproperly-polarized diode and the switched-on controllable switch, intothe primary winding when the voltage (U_(C2)) of the second capacitorhas become greater than that (U_(C1)) of the first capacitor during itsdischarge.
 2. Ignition apparatus according to claim 1, wherein thecapacity of the second capacitor is approximately 2 to 5 times thecapacity of the first capacitor.
 3. Ignition apparatus according toclaim 1, wherein the voltage (U₂ in FIG. 1, U₁ in FIG. 2) that chargesthe first capacitor is greater, than the voltage (U₁ in FIG. 1, U₂ inFIG. 2) that charges the second capacitor.
 4. Ignition apparatusaccording to claim 1, wherein the first capacitor is charged by aseparately supplied voltage (U₂).
 5. Ignition apparatus according toclaim 1, wherein the second capacitor { is charged by aninternally-obtained voltage (U₂ in FIG. 2) that is smaller, by thevoltage difference of a Zener diode, than the voltage (U₁) with whichthe first capacitor is charged.
 6. Ignition apparatus according to claim1, wherein resistors are provided in series with the first and secondcapacitors, with the aid of which resistors the time constants of thecharging of the capacitors is selected, with consideration of the energyrequired for igniting the high-pressure gas discharge lamp andtransferring it into the burning operation such that the desired voltageis attained at the second capacitor when the controllable switch closes.7. Ignition apparatus according to claim 1, wherein the controllableswitch is a spark gap that switches on when a certain voltage isattained.
 8. Ignition apparatus according to claim 1, wherein avoltage-limiting element is provided between the input terminals of theignition apparatus for closing the ignition-current path.
 9. Ignitionapparatus according to claim 3, wherein the voltage that charges thefirst capacitor is about 2 to 3 times greater than the voltage thatcharges the second capacitor.
 10. Ignition apparatus according to claim8, wherein the voltage limiting element is a varsity.